DULUTH, Minn. (AP) -- Officials at Lake Superior Zoo don't know what caused the death of a cantankerous but beloved llama known as "Dolly."

Dolly died Monday night. She was 12 years old.

Peter Pruett, the zoo's director of animal management, tells the Duluth News Tribune (http://bit.ly/rzggOd) that Dolly showed signs of illness on Sunday. The zoo's veterinarian and animal care staff attended to her, but she continued to deteriorate during the day on Monday.

The llama's body was sent to the University of Minnesota for a necropsy, or animal autopsy.

Dolly appeared in several of the Duluth zoo's commercials.